simplify

Author: kentcdodds

exercises/03.advanced-tools/03.problem.errors/README.mdx renamed to exercises/02.tools/03.problem.errors/README.mdx

@@ -5,21 +5,6 @@ wrong—maybe a user tries to fetch a journal entry that doesn't exist, or there
 a problem saving data. It's important that both users and LLMs get clear,
 structured feedback when errors happen.
 
-For this step:
-
-- Update your tools to return error responses in a way that's compatible with
-  the MCP spec.
-- Make sure errors are surfaced in the response, with `isError: true` and a
-  helpful message in the content.
-
-This will make your journaling app more robust and user-friendly, and help LLMs
-handle problems gracefully.
-
-<callout-info>
-	ℹ️ In this exercise, you can simulate an error by trying to submit a tag with
-	the word "error" in the name.
-</callout-info>
-
 Example error response:
 
 ```json
@@ -38,4 +23,12 @@ Example error response:
 }
 ```
 
+Luckily for us, the MCP TypeScript SDK handles errors automatically. So all you
+need to do is throw an error from your tool, and the SDK will handle the rest!
+
+For this step, we're going to say that tag names cannot include the word
+"error". If it does, throw an error with a descriptive message and then try it
+out in the inspector. You'll notice the `isError` field is set to `true` and the
+content is the helpful error message you provided.
+
 - [📜 MCP Spec: Errors](https://modelcontextprotocol.io/specification/2025-03-26/server/tools#error-handling)

exercises/05.prompts/01.problem.prompts/package.json renamed to exercises/02.tools/03.problem.errors/package.json

@@ -1,5 +1,5 @@
 {
-  "name": "exercises_05.prompts_01.problem.prompts",
+  "name": "exercises_02.tools_03.problem.errors",
   "private": true,
   "type": "module",
   "scripts": {

exercises/03.advanced-tools/01.problem.db/src/index.test.ts renamed to exercises/02.tools/03.problem.errors/src/index.test.ts

@@ -1,12 +1,6 @@
 import { McpServer } from '@modelcontextprotocol/sdk/server/mcp.js'
 import { StdioServerTransport } from '@modelcontextprotocol/sdk/server/stdio.js'
 import { z } from 'zod'
-// 🐨 bring in the database and initialize it.
-// 💰 here's the import:
-// import { DB } from './db/index.ts'
-
-// 💰 Here's how you initialize the database:
-// const db = DB.getInstance('./db.sqlite')
 
 const server = new McpServer(
 	{
@@ -17,25 +11,20 @@ const server = new McpServer(
 		capabilities: {
 			tools: {},
 		},
-		// 🐨 update the instructions to describe a journaling app
 		instructions: 'This lets you solve math problems.',
 	},
 )
 
 server.tool(
-	// 🐨 rename this tool to `create_tag`
 	'add',
-	// 🐨 update the description to describe a tool that creates a tag for entries
 	'Add two numbers',
-	// 🐨 update the arguments to take a name and description as arguments (💯 add a description to each argument)
 	{
 		firstNumber: z.number().describe('The first number to add'),
 		secondNumber: z.number().describe('The second number to add'),
 	},
-	// 🐨 accept the tag as an argument
 	async ({ firstNumber, secondNumber }) => {
-		// 🐨 create the tag:
-		// 💰 const createdTag = await db.createTag(tag)
+		// 🐨 throw an error if the second number is negative
+		// 💯 as a bonus, you can use the invariant function from @epic-web/invariant
 		return {
 			content: [
 				{

exercises/03.advanced-tools/01.problem.db/src/index.ts renamed to exercises/02.tools/03.problem.errors/src/index.ts

@@ -1,5 +1,5 @@
 {
-  "name": "exercises_06.sampling_01.problem.simple",
+  "name": "exercises_02.tools_03.solution.errors",
   "private": true,
   "type": "module",
   "scripts": {

exercises/03.advanced-tools/01.problem.db/tsconfig.json renamed to exercises/02.tools/03.problem.errors/tsconfig.json

@@ -0,0 +1,48 @@
+import { invariant } from '@epic-web/invariant'
+import { McpServer } from '@modelcontextprotocol/sdk/server/mcp.js'
+import { StdioServerTransport } from '@modelcontextprotocol/sdk/server/stdio.js'
+import { z } from 'zod'
+
+const server = new McpServer(
+	{
+		name: 'EpicMe',
+		version: '1.0.0',
+	},
+	{
+		capabilities: {
+			tools: {},
+		},
+		instructions: 'This lets you solve math problems.',
+	},
+)
+
+server.tool(
+	'add',
+	'Add two numbers',
+	{
+		firstNumber: z.number().describe('The first number to add'),
+		secondNumber: z.number().describe('The second number to add'),
+	},
+	async ({ firstNumber, secondNumber }) => {
+		invariant(secondNumber >= 0, 'Second number cannot be negative')
+		return {
+			content: [
+				{
+					type: 'text',
+					text: `The sum of ${firstNumber} and ${secondNumber} is ${firstNumber + secondNumber}.`,
+				},
+			],
+		}
+	},
+)
+
+async function main() {
+	const transport = new StdioServerTransport()
+	await server.connect(transport)
+	console.error('EpicMe MCP Server running on stdio')
+}
+
+main().catch((error) => {
+	console.error('Fatal error in main():', error)
+	process.exit(1)
+})